Study On Defect Indentification And Evaluation Method Of Exterior Thermal Insulation System Based On Infrared Thermal Image

The large-scale application of external insulation is of great significance to building energy conservation.However,the service life of the existing external thermal insulation system cannot match the main body of the building,resulting in various defects.The thermal insulation boards often fall off,which brings great threat to the city safety.The existing detection methods are basically completed by manpower,which are inefficient,costly and inaccurate,and cannot realize the batch detection of external insulation system of external walls.Therefore,it is very necessary to develop an efficient,economical and accurate detection method for external insulation defects of external walls.Taking the exterior insulation system of exterior wall in Harbin area in winter as the research object,this paper developed a defect identification and judgment method of exterior insulation system based on infrared thermal image.Experiments were carried out on the scale model of the external insulation system under laboratory conditions,and the infrared images of the artificial defects of the external insulation system under the action of internal and external temperature difference were obtained,and the types of defects that could be identified through the infrared images under laboratory conditions were identified.The external insulation system of exterior wall of existing buildings in Harbin area was investigated under low temperature in winter,and the defect types of external insulation which could be identified by infrared image in actual engineering were identified.By using Python-Open CV image mosaicing is explored,visible and infrared image mosaicing is carried out.It is found that it is difficult to extract enough feature point pairs from the image when the area with rich features,such as windows,is not included,and good mosaicing effect cannot be obtained.This paper presents a method to identify and judge defects of external thermal insulation of exterior walls,and develops a corresponding program to identify and judge defects.The method is divided into five parts: image preprocessing,temperature anomaly area determination,actual size calculation of exterior walls,defect determination and location,defect area and damage degree calculation.Gaussian denoising is used to preprocess the image to eliminate some invalid information and improve the recognition accuracy.By studying four coordinate systems in the field of computer vision,the actual size of external thermal insulation system is calculated.Canny edge detection and contour extraction algorithm are used to outline the temperature anomaly area in the infrared image.Combined with the morphological characteristics of defects and common thermal bridges in the infrared image,the classification of temperature anomaly area and defect determination are realized.Combined with the calculation of the actual size of the image,the location of defects is realized.The damage degree and defect area are calculated by using threshold segmentation algorithm.In this paper,a comprehensive evaluation system construction and grade evaluation method based on analytic hierarchy process(AHP)are proposed.Combining qualitative and quantitative methods,the comprehensive evaluation system of external thermal insulation system for external walls is established,and the grade evaluation method is formulated.Taking the comprehensive evaluation of external thermal insulation system of molded polystyrene board and thin plastered exterior wall as the research object,three sub-layers of external thermal insulation system and material durability,defects of building exterior wall system and bond performance and wind load resistance were selected.The sub-layer evaluation items were separated out and the quantitative classification standard was determined.Based on the corresponding criteria,the quantitative index of sub-layer was determined and the evaluation factor set was established.Combined with the characteristics of external thermal insulation system of external wall,the method of 5-grade variable length partition was adopted to divide the single index value into 5 grades in the range,and the evaluation grade set was obtained.Then the evaluation matrix was established to determine the weight of each index layer,and the comprehensive score of exterior insulation system was obtained.Finally,according to the comprehensive score,the evaluation status of external insulation system is obtained,and the maintenance suggestions are put forward.This study provides ideas for defect determination and grade assessment of external insulation system of external walls in engineering,and has certain guiding significance for improving the efficiency and accuracy of detection methods and putting forward maintenance suggestions.